This invention relates to sunscreening compositions for application to the skin, and more particularly to sunscreen products which are protected against microbial proliferation using the biocide chlorphenesin.
Sunscreening compositions are increasingly being considered as essential protectants for persons spending significant amounts of time in outdoor areas during daylight hours. The incidence of skin damage from actinic solar radiation, including skin aging, solar keratoses and various types of cancerous lesions is quite high, and it is generally recognized that many of these conditions have their origins in exposure to ultraviolet wavelength radiation.
Many sunscreen products are emulsions such as lotions and creams, either of the oil-in-water type or the water-in-oil type. Such systems can be subject to microbial proliferation during storage and use, the microorganisms being introduced from the environment, container or ingredients during manufacture or from the environment during use, as the container is repeatedly opened and closed.
Other commercial products are sunscreen oils, preferred by some consumers over the more common emulsion products. These also are subject to microbial contamination during manufacture and use. Therefore, it is customary to include one or more biocidal ingredients in the compositions to avoid problems such as product viscosity changes, pH changes, emulsion breakdown, visible microorganism growth, color changes, disagreeable odor formation and user skin reactions that may be caused by microbes.
A biocide, sometimes referred to as a xe2x80x9cpreservativexe2x80x9d or xe2x80x9cantimicrobial,xe2x80x9d component of a product should ideally have a broad spectrum of activity, since the product could be exposed to many different classes of bacteria, yeast, mold and other types of contaminants. As microorganisms usually require water for their existence and proliferation, biocides are typically chosen to be soluble in the aqueous phase of an emulsion; sometimes, a biocide having water solubility below its biocidal-effective concentration can be dissolved in a cosolvent, and the resulting solution added to the aqueous phase for preparing an emulsion.
Chlorphenesin, having the chemical name 3-(4-Chlorophenoxy)-1,2-propanediol and the formula C9H11ClO3, is a broad-spectrum biocide that has been used in cosmetic-type products. It has a very low water solubility and commonly is dissolved in cosolvents, including alcohol, diol and triol cosolvents (collectively referred to hereinafter as xe2x80x9calcoholsxe2x80x9d) having a high water solubility, such as ethanol, phenoxyethanol, glycerin, propylene glycol, butylene glycol and others. When so dissolved, biocidal-effective amounts of chlorphenesin can then be solubilized in the aqueous phase of an emulsion product. However, this extra step of dissolution in the cosolvent is not convenient and adds to the manufacturing cost and complexity of the product, including requirements for raw material storage and documentation. Further, such cosolvent ingredients may add undesired properties to a particular product or may not be compatible with other desired ingredients.
The present invention includes a method for preparing sunscreen products that contain chlorphenesin, wherein the chlorphenesin is added directly to the water-insoluble xe2x80x98oilxe2x80x99 phase components before an emulsion is formed. The invention also includes sunscreen products that do not contain water as an ingredient, i.e., sunscreen oils, wherein chlorphenesin is added as a preservative component. Typically, the chlorphenesin is added to a water-insoluble mixture that contains the organic sunscreen active ingredients.
The invention further includes sunscreening emulsion compositions that are prepared to at least initially contain chlorphenesin in the water-insoluble phase.
Also encompassed by the invention is a sunscreen composition containing chlorphenesin, having a substantial absence of alcohol cosolvents (as discussed below) for the chlorphenesin.
The preparation of sunscreen emulsions for skin application is generally well known, and typically involves generating an xe2x80x9caqueous phasexe2x80x9d by: combining water and water-soluble or water-dispersable ingredients to preferably, but not necessarily, form a solution; generating an xe2x80x9coil phasexe2x80x9d by combining water-insoluble ingredients to preferably, but not necessarily, form a solution; then combining the aqueous and oil phases, usually under shearing conditions created by stirring or simultaneously passing the phases through a pumping device. If ingredients which are not soluble in either phase (such as particulate inorganic materials) are to be included in a product, they usually are dispersed in the phase where they will form the more stable dispersion, before the phases are combined. Many permutations of this general process are known, including the use of elevated temperatures for one or both phases, and the present invention is not to be restricted to any particular preparative method.
The resulting emulsions, commonly in the form of lotions or creams, are dispersions of fine droplets of one phase in a more or less continuous body of the other phase. Ingredients which are not soluble in either phase usually have an affinity for one of the phases, preferably the phase which is considered to be the xe2x80x9cinternalxe2x80x9d phase. Formation and stability of the emulsion are enhanced by the inclusion of ingredients having surfactant properties; such components are known as emulsifiers and emulsion stabilizers. Numerous useful emulsifiers are listed at pages 1795-1803 in Volume 2 of J. A. Wenninger et al., International Cosmetic Ingredient Dictionary and Handbook, Eighth Edition, The Cosmetic, Toiletry, and Fragrance Association, Washington, D.C., 2000 (hereinafter referred to as xe2x80x9cthe CTFA bookxe2x80x9d). Many useful emulsion stabilizers are listed at pages 1742-1743 of that same book. Those skilled in the art of emulsion product preparation are fully aware of the considerations in selecting suitable emulsification ingredients for forming a stable emulsion system.
In addition to emulsion products, sunscreen oils are also popular with many consumers. These products do not have water as an added component, but may contain some moisture as an impurity in one or more of the ingredients. Generally, any water will be present in the oil products in very small concentrations; these products are considered to be substantially free of water.
Sunscreen compositions of the invention contain one or more organic sunscreen active ingredients. Those active ingredients which are presently approved by regulatory agencies in the United States include: Dioxybenzone, Oxybenzone, Sulisobenzone, Avobenzone, Cinoxate, Diethanolamine methoxycinnamate, Digalloyl trioleate, Ethyl 4-[bis(hydroxypropyl)] aminobenzoate, Padimate O, Octyl methoxycinnamate, Octyl salicylate, Glyceryl aminobenzoate, Homosalate, Menthyl anthranilate, Octocrylene, Aminobenzoic acid, Phenylbenzimidazole sulfonic acid and Trolamine salicylate. There are other active ingredients that have been accepted for use in other countries and several additional ingredients have been proposed for acceptance. All such active ingredients are considered to be useful in the present invention.
Chlorphenesin will not necessarily be the sole biocidal preservative in the sunscreening compositions of the invention. Other components having the same function, including those listed at pages 1765-1766 in the CTFA book, Volume 2, may be included in the compositions as needed.
Sunscreening products frequently contain other components, many of which impart cosmetic elegance to the composition. These components include emollients, humectants and other skin-conditioning agents, film formers, fragrances, agents affecting viscosity, colorants, pH adjusters and buffers, skin protectants and others. Many useful components are described in the volumes of the CTFA book, and their selection and amounts for a particular product are well within the ordinary skill in the art.
To prepare the products of the invention, the chlorphenesin biocide is included as a component of a water-insoluble phase. Chlorphenesin powder typically will be added to a solution or dispersion that includes the organic sunscreen active ingredients and may be among the later added ingredients for the oil phase, since it is a minor concentration component and can be dispersed more easily if added to a large amount of other ingredients. In many procedures, the combinations constituting the oil and/or aqueous phases will have been heated to facilitate solubilities of certain components, or to enhance emulsion formation when the phases are combined, and chemical stability of the chlorphenesin will be enhanced by cooling the oil phase combination to less than about 65xc2x0 C. before the chlorphenesin is added and then avoiding any subsequent heating of the mixture to higher temperatures. The final sunscreen product usually will contain about 0.1 to about 1 percent by weight chlorphenesin; a more typical amount for a sunscreen product is about 0.1 to about 0.3 percent by weight.
After an emulsion product has been formed, a certain amount of the chlorphenesin can migrate to the aqueous phase and effectively control microbial concentrations in that phase. However, it is a characteristic of the invention that all of the chlorphenesin will have been initially introduced into the emulsion product as a component of the oil phase. Further, it is a feature of the invention that the chlorphenesin will not be dissolved in any solvent before it is added to the oil phase mixture.
The invention will be further illustrated by the following examples of sunscreen product compositions, where concentrations are weight percentages and, where possible, the names of the components are taken from the CTFA book. It is not intended that these examples will limit the scope of the invention, as established solely by the appended claims.